Bicycloheptadiene dimerization



United States Patent 3,326,993 BICYCLOHEPTADIENE DIMERIZATION Bruce N.Bastian, Lafayette, and Gerhard N. Schrauzer, Orinda, Calif., assignorsto Shell Oil Company, New

York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 20, 1965,Ser. No. 499,000 9 Claims. (Cl. 260-666) This invention relates to animproved method for the dimerization of bicycloheptadiene and to a noveldimer thereby produced.

Methods are known in the art for the dirnerization ofbicyclo(2.2.1)hepta-2,5-diene, herein for brevity termedbicycloheptadiene, to produce polycyclicdimer derivatives. Bird et al.,Chem. and Ind.; 20 (1960), disclose the reaction of bicycloheptadienewith certain metal carbonyls, e.g., iron carbonyl, to producebicycloheptadiene dimers together with major amounts of ketone products.The bicycloheptadiene dimers of Bird et al. are ethylenicallyunsaturated, containing from 1 to 2 ethylenic linkages per molecule. Asaturated bicycloheptadiene dimer is disclosed by Lemal et al.,Tetrahedron Letters, 11, 268 (1961). Although the structure of thesaturated dimer of Lemal et al. was not established with certainty, itis evident that the bicycloheptadiene moieties were joined by fourseparate carbon-carbon bonds as the product obtained was free fromethylenic unsaturation and was free from cyclopropane ring moieties,e.g., nortricyclene moieties. In co-pending application of Miiller etal., US. Ser. No. 457,787, filed May 21, 1965, now issued as US. PatentNo. 3,282,663, there is disclosed and claimed certain compositions,useful as high energy fuels, which comprise mixtures of severalunsaturated bicycloheptadiene dimers. These compositions are useful ashigh energy fuels, particularly as fuels for jet aircraft, because ofthe relatively high heat of combustion per unit volume of the dimercompositions which renders the compositions eminently suitable forapplications wherein a volume savings is required. It would, however, beof advantage to provide a bicycloheptadiene dimer of an even greaterheat of combustion per unit volume.

It is an object of the present invention to provide an improved methodfor the dimerization of bicycloheptadiene and to provide the novelsaturated bioycloheptadiene dimer thereby produced. More particularly,it is an objectto provide the novel bicycloheptadien dimerheptacyclo(5.3.1.1 .1 .1 0 0 )tetradecane and .a method for theproduction thereof.

It has now been found that these objects are accomplished by contactingbicycloheptadiene with certain cohalt-containing carbonyl catalysts,customarily in the presence of an acidic co-catalyst, in liquid-phasesolution in an inert non-polar reaction solvent. The process of theinvention results in the formation of a dimer product containing majorproportions of the saturated heptacyclortetradecane dimer, and in someinstances results in the exclusive formation of this saturated dimer.

The novel dimer of the invention is heptacyclo (5.3.1.1 .1 .l .0 .0)tetradecane which is depicted by the structural formula wherein theadded numerals indicate one conventional method of identifying therelative locations of the carbon atoms present. Although it is apparentthat the possibility 3,326,993 Patented June 20, .1967

ice

, melting point of 65.065.6 C. and is believed to be the endo-cis-endoformula.

isomer represented by the following The process of the inventioncomprises dimerizing ibicycloheptadiene in the presence of certainco'baltcontainmg carbonyl catalysts and inmost instances in the presenceof a Lewis acid co-catalyst. Catalysts thatare suitably employed in theprocess of the invention are represented by the formula wherein M iszinc, cadmium or indium, m is a whole number from 0 to 1 inclusive and nis a whole number from 2 to 3 inclusive equal to the valence of themetal M, with the proviso that when m=-0, then n=2. These catalysts aredicobalt octacarbonyl and zinc, cadmium or indiumtetracarbonylcobaltate. Preferred catalysts of the above formulaarethose wherein m==1 and M is a metal of Group IIB of the PeriodicTable of an atomic number from 30 to 48 inclusive, that is, M is zinc orcadmium. Particularly preferred as catalyst is zinctetracarbonylcobaltate, Zn[Co(CO) The cobalt-containing carbonylcatalyst is employed in catalytic quantities. The amount of catalyst isnot critical, except insofar as the ratio of catalyst tobicycloheptadiene does influence the relative proportion of theheptacyclotetradecane in the product mixture. In order to obtainaproduct.mixturecontaining substantial proportions of theheptacyclotetradecane product, a molar ratio of catalyst tobicycloheptadiene .of at least 1:1'000 is'preferred. There does notappear to be a critical upper limit on the relative amount of catalystto beutilized, however molar ratios of catalyst tobicycloheptadiene,greater than about 1:10 do not appear to offer anyfurther practical advantage that would compensate for the additionalexpense. Best results are obtained when molar ratios of catalyst tobicycloheptadiene of from about 1:100 to about 1120 are utilized.

The cobalt-containing carbonyl catalyst is employed in conjunction withan acidic co-catalyst. The acidic materials suitably utilized .toimprove the efficiency of the process, particularly the selectivity toheptacyclotetradecane product are generically characterized as Lewisacids. By the term Lewis acid is meant a material having .the ability toaccept an electron pair during coordination with materials normallyconsidered to be bases and having the ability to donate an electronpair. One class of Lewis acids is characterized as the salt of a weakbase and a strong acid, the base being a metallic base wherein the metalis a member of a group of the Periodic Table other than Groups IA andHA, and the acid being a strong acid which is a non-oxidizing,mono-basic acid, preferably a hydrogen ,halide. The latter class ofLewis acids, i.e., metal salts of hydrogen halides, are covalent metalhalides wherein the metal-halogen bond exhibits a substantial degree ofcovalent character rather than an essentially exclusively ioniccharacter, and the covalent metal halides are on occasion referred to asFriedel-Crafts catalysts because of the ability of these covalent metalhalidesto catalyze Friedel-Crafts alkylation or 'acylation processes.Particularly preferred as the Lewis acid e0 catalysts of the inventionare covalent metal halides wherein the halogen has an atomic number offrom to 35, that is, the halogen is fluorine, chlorine or bromine.Illustrative of covalent ametal halides suitably employed asc-o-catalyst are boron trifluoride, aluminum chloride, aluminum bromide,stannous chloride, arsenic trichloride, antimony pentafluoride, titaniumtetrachloride, ferric chloride, cobalt bromide, palladium chloride,platinum chloride, cupric fluoride, zinc chloride, zinc bromide, cadmiumchloride and the like. The covalent metal halides are preferablyemployed as such, although it is also useful to employ acidic complexesof the covalent metal halides, e.g., etherates or complexes with organicnitriles.

The catalyst and co-catalyst are typically employed in a molar ratio ofcatalyst to co-catalyst of from about 2:1 to about 1:15 with molarratios of catalyst to co-catalyst of from about 1:1 to about 1:8 beingpreferred. A special case is observed when the catalyst employed is acompound'of the formula wherein M is zinc or cadmium. In these instancesit has been found that the process is operable in the substantialabsence of co-catalyst. Therefore, when a zinc or cadmiumtetracarbonylcobaltate catalyst is employed, molar amounts ofco-catalyst up to about 15 moles of co-catalyst per mole of the zinc orcadmium catalyst are suitable with molar amounts up to 8 moles ofco-catalyst per mole of zinc or cadmium catalyst being preferred.

The dimerization is conducted in liquid-phase solution in an inertnon-polar reaction solvent and solvents which are liquid at reactiontemperature and pressure, which are essentially non-polar in characterand are inert towards the bicycloheptadiene reactant and the dimerproduct are satisfactory. Preferred non-polar solvents comprise thehydrocarbons, particularly hydrocarbons free from aliphatic unsaturationincluding alkanes such as hexane, heptane, isooctane, decane anddodecane; cycloa'lkanes such as cyclohexane, cyclopentane,methylcyclopentane and decahydronaphthalene; and aromatic hydrocarbonsincluding benzene, toluene, xylene, ethylbenzene and cumene.

The method of effecting dimerization is not critical. In onemodification, the entire amounts of bicycloheptadiene, catalyst,co-catalyst if employed, and reaction solvent are charged to anautoclave or similar reactor and the mixture is maintained at reactiontemperature and presure until reaction is complete. It is also useful toadd one reaction mixture component to the others in increments, as bygradually adding the bicycloheptadiene to a mixture of the solvent andcatalyst system. In yet another modification, the dimerization isconducted in a continuous manner as by contacting the bicycloheptadieneand catalyst system during passage through a tubular reactor. In anymodification, the reaction is conducted at a somewhat elevated reactiontemperature. Temperatures from about 40 C. to about 150 C. are generallysatisfactory with the temperature range from about 50 C. to about 130 C.being preferred. Reaction pressures which are atmospheric,subatmospheric or superatmosphe-ric are suitably employed provided thatthe reaction mixture is maintained substantially in the liquid phase.Little advantage appears to arise from utilization of pressures whichare substantially different from atmospheric and the use ofsubstantially atmospheric pressure, e.g., from about 0.5 atmosphere toabout atmospheres, is preferred.

In order to maintain a high degree of catalyst selectivity toward theformation of heptacyclotetradecane product, the reaction is conducted inan inert, non-basic reaction environment. Thus, it is preferred toeffect dimerization in an oxygen-free, substantially anhydrous reactionenvironment in the substantial absence of basic materials.

Subsequent to reaction, the product mixture is separated and recoveredby conventional means, as by selective extraction, fractionaldistillation, fractional crystallization or the like. For someapplications, however, separation of individual catalyst components isnot necessary as the product mixture, upon removal of solvent, is usefulas such.

The product mixture comprises essentially the abovedepictedheptacyclotetradecane with varying amounts of unsaturatedbicycloheptadiene dimers depending upon the precise reaction conditionsemployed as well as the particular ratios of reactant to catalyst and/orco-catalyst. However, the heptacyclotetradecane product is separablefrom any other dimer products produced and in some instances is the soledimer product.

As previously stated, the broad class of bicycloheptadiene dimers isuseful as a high energy fuel. Several criteria are useful in determiningthe value of a fuel in such an application, among which is the heat ofcombustion per unit volume of the fuel as well as the thermal stability.The above-identified copending application of Miiller et al. describesand claims certain mixtures of bicycloheptadiene dimers useful as highenergy fuels. A typical mixture of dimers of the Miiller .et al.application comprises about 21.9% :by weight of dimers represented bythe general formula pentacyclo(8.2.1.1 .0 0 )tetradeca-5,1 l-diene andabout 76.3% by weight of .dimers of the formula hexacyclo(7.2.l.1 .1 .0.0 )tetradec-lO-ene This mixture is characterized by a density of 1.0904g./ ml. at 20 C. and a gross heat of combustion of 11,310 cal/ml. Incontrast, the heptacyclic dimer of the present invention has asubstantially greater density, 1.258 g./rn1. at 25 C., as Well as asubstantially higher gross heat of combustion per unit volume, 12,932cal./ml. In addition the heptacyclotetradecane product is characterizedby a greater degree of thermal stability than either theabove-identified pentacyclic or hexacyclic dimers, both of which undergoextensive pyrolysis at or below about 350 C., in contrast to theheptacyclic dimer of the invention which is thermally stable attemperatures at least as high as 445 C.

To further illustrate the improved process of the invention and thenovel product thereof, the following examples are provided. It should beunderstood that the details thereof are not to be regarded aslimitations as they may be varied as will be understood by one skilledin this art.

EXAMPLE I The zinc tetracarbonylcobaltate employed in the followingexamples was prepared by charging to an autoclave 12 g. of zinc dust and400 ml. of a 10% solution of dicobalt octacar-bonyl in toluene. Carbonmonoxide was introduced to give a 3000 p.s.i. pressure (20 C.) and theautoclave was heated and maintained at 200 C. and 4750 p.s.i. for 12hours. The reactor was then cooled and vented and the yellow solutionwas transferred under nitrogen to a low temperature crystallizer. Theyield of Zn[Co(CO) a yellow crystalline solid, was 30.95 g.

By similar procedures, In [Co(CO) and )4]2 were prepared.

EXAMPLE II To a nitrogen-filled reactor was charged 10 0 ml. of toluene,0.81 g. of zinc tetracarbonylcobaltate and 2.28 g. of boron trifluorideetherate. The reaction mixture was swept with nitrogen and was stirredwhile 226 g. of bicycloheptadiene was added and the reaction mixture washeated to 70 C. After the addition was complete, the mixture wasmaintained at 70-80 C. for 21 hours. The product mixture was removed,washed with 5% aqueous sodium carbonate, dried over anhydrous sodiumcarbonate, decolorized with activated carbon and finally distilled atreduced pressure. The

heptacyclo(5.3.1.1 .1 .1 0 )tetradecane B.P. 73 C. at 1-2 mm. wasobtained in a yield of 76.4% 5 based upon the bicycloheptadiene charged.The product, upon recrystallization from ethanol, had a melting point of65.0-65.6 C. and had the following elemental analysis.

Analysis.Calc. (weight percent): C, 91.3; H, 8.7.

Found: C, 91.3; H, 8.8.

6 in the presence of various catalysts and in the presence or absence ofvarious Lewis acid oo-catalysts. The results of this series are shown inTable III wherein the heading M refers to any additional metal portionof the catalyst and the term mmole represents millimoles. In each casethe percent by weight in the product mixture of the heptacyclic dimerwas determined as well as the per-cent by weight of unreactedbicycloheptadiene.

TABLE III Time, Temp., Unreacted bi- Heptacyclic M, mole Lewis acid,mmole hr. C. cycloheptadimer,

diene, percent percent wt.

4 100 0 100 0. 1 40 6. 0 88. 5 N 4. 1 100 11. 1 50. 3 Cd, 0.5---. B1 30(CzHsh, 0.71..-" 0. 100 0 100 Zn, 1.0..... PtC 2(CGH5C/N)z, 1.0-. 0.1110 0 100 Cd, 0.5-... PdCl2(CsH5CN)2, 0.5.. 72 100 9.0 91. 0 None, 1.0..B 3, 0.5 2 70 6.8 93.2 None, 0.5-. AlBr 0.5 1 60 0 00 The structure ofthe product was confirmed by mass spectrometric analysis and by thenuclear magnetic resonance spectrum which was consistent with the abovestructure. The infrared analysis showed a band at 12.53 characteristicof nortricyclene absorption and did not contain absorptionscharacteristic of olefinic linkages.

EXAMPLE III The procedure of Example II was employed in the dimerizationof 5 ml. of bicycloheptadiene in the presence of varying amounts of zinctetracar-bonylcobaltate as catalyst in 10 ml. of toluene as solvent. Theresults of this The procedure of Example II was repeated employingvarious ratios of boron trifluoride etherate co-catalyst to zinctetracarbonylcobaltate catalyst. In each case the conversion ofbicycloheptadiene to the heptacyclic dimer was determined as a functionof the molar quantity of the zinc-containing catalyst. The results ofthis series are shown in Table 11 wherein the heading Ratio refers tothe molar rati-o of co-catalyst to catalyst and the heading MolesConverted refers to the number of moles of bicycloheptadiene convertedto the heptacyclic dimer product per mole of the catalyst present.

TABLE II Ratio Moles converted EXAMPLE V The procedure of Example II wasfollowed to effect dimerization of bicycloheptadiene under varyingconditions We claim as our invention: 1. The process of producing aheptacyclo(5.3.1.1 .1 .1 .0 .0 )tetradecane as the majorbicycloheptadiene dimer product by intimately contactingbicyclo(2.2.1)hepta-25 diene with (a) from about 0.001 mole to about 0.1mole per mole of said bicycloheptadiene of the cobalt-containingcarbonyl catalyst of the formula wherein M is zinc, cadmium or indium, mis a whole number from 0 to 1 inclusive and n is a whole number from 2to 3 inclusive equal to the valence of the metal M, with the provisothat when mi=0 then n=2, and (b) from about 0.5 mole to about 15 molesof Lewis acid co-catalyst per mole of said cobalt-containing carbonylcompound; in liquid-phase solution in inert non-polar hydrocarbonreaction solvent, at a temperature of from about 40 C. to about C., in asubstantially anhydrous, non-basic reaction environment.

2. The process of claim 1 wherein the Lewis acid cocatalyst is acovalent metal halide wherein the halogen is halogen of atomic numberfrom 9 to 35.

3. The process of claim 2 wherein m=0.

4. The process of claim 2 wherein m: 1.

5'. The process of claim 2 wherein the catalyst is M[Co(CO) wherein M iszinc or cadmium.

6. The process of claim 5 wherein the process is conducted in thesubstantial absence of the cocatalyst.

7. The process of claim 5 wherein the co-catalyst is boron trifluoride.

8. The process of claim 5 wherein the co-catalyst is antimonypentafluoride.

9. The compound heptacyclo(5.3.1.1 .1 .1 0 0 ")tetradecane characterizedby a melting point of 65.0-65.6 C.

References Cited C. W, Bird et al., (1) Chem. & Ind., pages 20-21, 1960.C. W. Bird et al., (1) Tetrahedron Letters, No. 11, pages 373-375, 1961.

David M. Lemal et al., Tetrahedron Letters, No. 11, pages 368-372, 1961.

DELBERT E. GANTZ, Primary Examiner.

V. OKEEFE, Examiner.

1. THE PROCESS OF PRODUCING A